The present invention relates to a contact keyboard for a typewriter or other office machine and to a method of manufacturing the keyboard. The keyboard according to the invention is of the type set forth in the introductory part of claim 1.
Such a keyboard is known from DE-A 2309041. This keyboard has a good feel and has some advantages associated with the modularity of the keys. However it suffers from the drawback of being rather costly as it requires the assembly of the keys one-by-one.
A keyboard is also known from US 4315114 in which the actuators are connected together by resilient hinge arms cantilevered from a common cross member and which assist the domes in returning the key after it is released. Such a keyboard does not provide the good feel required for a typewriter keyboard.
The object of the present invention is to provide a contact keyboard which has a limited number of parts to be assembled and which is reliable and inexpensive and moreover gives the good feel required for a typewriter keyboard.
In accordance with this object, the keyboard according to the invention is characterised in the manner set forth in claim 1. The invention further provides a method of manufacturing as set forth in claim 4.
The invention will now be described in more detail, by way of example, with reference to the accompanying drawings, in which:
Referring to Fig. 1, the keyboard according to the invention comprises a plurality of keys 10 each of which has a cap 13 mounted on an actuator 11 which is slidable axially within a cylindrical recess 12 formed in a block 15 of thermoplastic material.
According to a characteristic of the invention, all the recesses 12 of the keyboard are formed in the block 15 (Fig. 2) by moulding.
The block 15 is mounted on a support plate 16 (Fig. 1) with the interposition of a mat 17 of sound-absorbing material, for example rubber. To facilitate the mounting of the block 15 on the plate 16, the block itself may be constituted by several elements 20 (Fig. 2), in each of which there is formed a plurality of recesses 12 and interconnected by flexible tongues 21 produced in one piece with the elements 20.
The actuators 11 are also of thermoplastic material, are formed in a cluster during a single moulding stage and are interconnected by sprues 30. The arrangement of the actuators 11 in the cluster corresponds to that of the recesses 12 in the block 15. The sprues 30 are suitable for being removed after the cluster of actuators 11 has been inserted in the corresponding recesses 12 in the block 15, as will be described later on.
An elastic element 22 (Fig. 1) constituted by a dome of silicone rubber in the form of an inverted cup is adapted to cooperate with the bottom part of each actuator 11. According to a first embodiment, the median section of each elastic element 22 is that illustrated in Fig. 3, while in a second embodiment each elastic element22 may have the median section of the type illustrated in Fig. 4. Each actuator 11 (Fig. 1) is urged by the corresponding elastic element 22 towards the sound-absorbing mat 17, against which it is arrested by two stop elements 18 of the actuator.
A cylindrical pad 23 (Figs. 1, 3, 4) of conductive silicone rubber is fixed to the inside of each dome 22 and is adapted to short-circuit two elements 24 and 25 of a printed circuit 26 when the key 10 is depressed, to generate in this way in known manner a corresponding electric signal. The shape of the elastic elements 22 ensures snap contact of the pad 23 on the elements 24 and 25.
The elastic elements 22 of the keyboard may be produced individually or formed in one or more rubber mats 28 (Figs. 5 and 6), in an arrangement corresponding to that of the recesses 12, by technologies known per se.
The method of manufacture of the keyboard hereinbefore described, which is one of the characteristics of the invention, is as follows.
The plate 16 is arranged on a work bench 40 (Fig. 7) and the mat 17 of sound-absorbing material is fixed to this plate. The block 15 with the recesses 12 is formed by moulding in a press 41 of known type and is thereafter mounted on the mat 17. In this way, the group A illustrated in Figure 8 is produced.
The group A so formed is placed in an apparatus 42 (Fig. 9) on which is also arranged the cluster of sliders 11 which has been formed by moulding in a press 43 of known type. The apparatus 42 inserts the sliders 11 automatically into the corresponding seats 12 in the block 15 and removes the sprues 30 therefrom. In this way, the group B illustrated in Fig. 10 is produced.
The group B so formed is placed in a machine 44 also prearranged for testing the keyboard itself. The elastic elements 22 are then arranged to correspond with the actuators 11. This is done with the aid of a tray 45 when each elastic element 22 is independent of the others, or by directly arranging the rubber mats 28 on the block 15.
Finally, the printed circuit 26 is mounted. Before fixing the printed circuit 26 to the block 15 and the plate 16 with screws, each single key 10 is tested by the machine 44 in any known manner.
After this last stage, the keyboard according to the invention is finished and ready to be packed.